1. Field of the Invention
The present invention relates to a magnetic reproducing apparatus having MR (magnetoresistive) heads, and particularly, to a magnetic reproducing apparatus capable of supplying an optimum sense current to each MR head for reproducing information recorded on a magnetic recording medium.
2. Description of the Related Art
Magnetic recording-reproducing apparatuses such as magnetic disk units and magnetic tape units employ combined heads each consisting of a wound thin-film magnetic head (inductive head) for recording information on a magnetic recording medium and an MR head for reproducing the recorded information.
The MR head has a magnetoresistive element whose resistance changes in response to an external magnetic field, to detect a leakage magnetic field due to magnetization reversal on a recording medium where information is recorded. When using the magnetoresistive element, a sense current is supplied thereto. Compared with the inductive head, the MR head is capable of providing a relatively large output that is proportional to a flux quantity from a recording medium, independently of a relative speed between the MR head and the recording medium. The MR head, therefore, is suitable for reproducing information from high-density recording tracks. If an optimum sense current is supplied, the MR head provides a large reproduced signal irrespective of a relative speed between the MR head and a recording medium such as a disk. The MR head is widely used because it satisfies requirements for increasing the capacity of high-density magnetic disk units used as external storage units of computers.
A magnetic reproducing apparatus having MR heads generally consists of a casing and a control board. The casing accommodates magnetic disks, a driving system for the magnetic disks, an actuator for writing and reading information to and from the magnetic disks through combined heads, and a head driving IC. The control board is attached to the outside of the casing and usually has a servo system for positioning the heads on tracks of the magnetic disks, a read-write circuit for decoding information read from the magnetic disks and writing information to the magnetic disks, a memory such as a ROM for storing a control program, a RAM for temporarily storing data, and a control circuit for carrying out various control tasks.
When a power source is turned on, the apparatus reads sense current values to be supplied to the MR heads from the memory on the control board and supplies sense currents accordingly to the MR heads to read various pieces of data from the magnetic disks. The sense current values stored in the memory are optimum values found through tests carried out in advance.
The sense current values stored in the memory will not be optimum for the MR heads if the control board is replaced due to a repair. If sense current values stored in the replaced control board are extremely high for the MR heads, they will shorten the service lives of the MR heads and deteriorate the reliability thereof.
To cope with this problem, there is a technique not to use the sense current values stored in the replacement control board. Instead, the technique unconditionally supplies small sense currents to the MR heads to read surface analysis (SA) data from the magnetic disks. The SA data contains sense current values to be supplied to the MR heads.
The small currents to read the SA data, however, are not optimum for the MR heads, and therefore, raise a problem of incorrectly reading the SA data from the magnetic disks.
An object of the present invention is to provide a magnetic reproducing apparatus capable of solving the problems of the prior art, always supplying optimum sense current to MR heads even if a control board is replaced, and improving the durability and reliability of the MR heads.
In order to accomplish the object, a first aspect of the present invention provides a magnetic reproducing apparatus having at least one recording medium for magnetically recording information, an MR head arranged for each recording surface of the recording media, a current supply circuit for supplying sense currents to the MR heads, respectively, so that each MR head may read information from the recording medium, and a decoder for decoding the read information. The magnetic reproducing apparatus consists of a resistance measuring circuit for measuring a resistance value of a magnetoresistive element of each MR head whenever a power source of the magnetic reproducing apparatus is turned on, a memory for storing a conversion table containing resistance values of magnetoresistive elements measured in advance and sense current values corresponding to the resistance values, and a sense current setter for reading, from the conversion table, sense current values corresponding to the resistance values of the MR heads measured by the resistance measuring circuit and setting the read sense current values in the current supply circuit, so that the current supply circuit keeps the set sense current values until the magnetic reproducing apparatus is turned off and supplies sense currents to the MR heads based on the set sense current values.
The first aspect is capable of setting proper sense currents for the MR heads according to the resistance values of the MR heads even if a control board attached to the magnetic reproducing apparatus is replaced.
In addition to the arrangement of the first aspect, a second aspect of the present invention employs a positioning mechanism for reading servo data from the recording media through the MR heads that receive the sense currents set by the sense current setter and positioning each MR head on a predetermined track on the recording medium according to the servo data a fetching circuit for reading surface analysis data from the predetermined track, fetching sense current data for each MR head from the surface analysis data, and storing the fetched sense current data, and a sense current resetter for resetting the sense current values in the current supply circuit to optimum ones for the MR heads based on the fetched sense current data.
The second aspect resets sense currents to be supplied to the MR heads according to surface analysis data that has been written in the recording media in advance, thereby ensuring the correctness of the sense currents to the MR heads even if the control board is replaced.
In addition to the arrangement of the second aspect, a third aspect of the present invention employs a comparator for comparing a casing number of the magnetic reproducing apparatus contained in the surface analysis data with a casing number of the magnetic reproducing apparatus stored in a nonvolatile memory arranged on the control board, and a prohibition circuit for prohibiting the sense current resetter from resetting the sense current values in the current supply circuit if a result of the comparison shows disagreement.
A fourth aspect of the present invention provides a magnetic reproducing apparatus having at least one recording medium for magnetically recording information, an MR head arranged for each recording surface of the recording media, a current supply circuit for supplying sense currents to the MR heads, respectively, so that each MR head may read information from the recording medium, and a decoder for decoding the read information. The magnetic reproducing apparatus consists of a nonvolatile memory arranged in a casing of the magnetic reproducing apparatus, for storing values of sense currents to be supplied to the MR heads, and a sense current setter for reading the sense current values from the nonvolatile memory when the magnetic reproducing apparatus is driven and setting the read values in the current supply circuit so that the current supply circuit supplies sense currents to the MR heads based on the set values.
The fourth aspect sets sense current values to be supplied to the MR heads according to sense current values stored in the nonvolatile memory arranged in the casing of the apparatus, thereby optimizing the sense currents to the MR heads even if a control board attached to the magnetic reproducing apparatus is replaced.
In addition to the arrangement of the fourth aspect, a fifth aspect of the present invention stores, in a nonvolatile memory, a program for reading surface analysis data from a predetermined track on a recording medium through an MR head.
In addition to the arrangement of the fifth aspect, a sixth aspect of the present invention employs a positioning mechanism for reading servo data from the recording media through the MR heads that receive the sense currents from the current supply circuit and positioning each MR head on a predetermined track on the recording medium according to the servo data, a fetching circuit for reading surface analysis data from the predetermined track, fetching sense current data for each MR head from the surface analysis data, and storing the fetched sense current data, and a sense current resetter for resetting the sense current values in the current supply circuit to optimum ones for the MR heads based on the fetched sense current data.
The sixth aspect resets sense currents to be supplied to the MR heads according to surface analysis data that has been written in the recording media in advance, thereby ensuring the correctness of the sense currents to the MR heads even if the control board is replaced.
A seventh aspect of the present invention is based on the second aspect and employs, as the sense current data for the MR heads contained in the surface analysis data, resistance values of the MR heads. According to the seventh aspect, the sense current resetter has a conversion table containing resistance values of MR heads and optimum sense current values corresponding to the resistance values, to convert the resistance values fetched from the surface analysis data into sense current values and reset the sense current values in the current supply circuit to the converted sense current values.
In addition to the arrangement of any one of the sixth and seventh aspects, an eighth aspect of the present invention employs a comparator for comparing a casing number of the magnetic reproducing apparatus contained in the surface analysis data with a casing number of the magnetic reproducing apparatus stored in a nonvolatile memory arranged on the control board, and a prohibition circuit for prohibiting the sense current resetter from resetting the sense current values in the current supply circuit if a result of the comparison shows disagreement.
In addition to the arrangement of the first aspect, a ninth aspect of the present invention employs a positioning mechanism for reading servo data from the recording media through the MR heads that receive the sense currents set by the sense current setter and positioning each MR head on a predetermined track on the recording medium according to the servo data, a nonvolatile memory arranged on the control board, for storing a conversion table containing MR head compositions and optimum sense current values corresponding to the compositions, a fetching circuit for reading surface analysis data from the predetermined track, fetching composition data for each MR head from the surface analysis data, and storing the fetched composition data, and a sense current resetter for reading optimum sense current values for the MR heads from the conversion table according to the fetched composition data and resetting the sense current values in the current supply circuit to the read optimum sense current values.
The ninth aspect sets an optimum sense current for each MR head according to the composition of the MR head.
The magnetic reproducing apparatus with MR heads of the present invention provides the following advantages:
(1) When configured to measure the resistance value of each MR head whenever turned on, read sense current values from a conversion table according to the measured resistance values, and set sense currents to the MR heads based on the read values, the apparatus is capable of supplying correct sense currents to the MR heads even if a control board attached to the apparatus is replaced.
(2) When configured to measure the resistance value of each MR head whenever turned on, read sense current values from a conversion table according to the measured resistance values, set sense currents to the MR heads based on the read values, fetch surface analysis data from recording media through the MR heads, and reset the sense currents to the MR heads according to sense current data contained in the surface analysis data, the apparatus is capable of supplying more correct sense currents to the MR heads even if the control board is replaced.
(3) When configured to employ a nonvolatile memory installed in the casing of the apparatus for storing sense current values for the MR heads, read the sense current values from the memory, and set sense currents to the MR heads based on the read values, the apparatus is capable of always supplying optimum sense currents to the MR heads even if the control board is replaced.
(4) When configured to employ a nonvolatile memory installed on the control board for storing a conversion table containing MR head compositions and sense currents corresponding to the compositions and read optimum sense currents from the table according to the compositions of the MR heads, the apparatus is capable of supplying sense currents that are optimum for the compositions of the MR heads.